The ability to quantify the world is essential for the most basic learning. The cognitive system responsible for this ability, the analog magnitude one, appears selectively impaired in a number of clinical populations (e.g., PD and Dyscalculia), making an understanding of this system a central issue in clinical psychology. Although both non-human animals and human infants are able to discriminate quantities, there is still much to learned about the nature and extent of their competence. Through comparative investigations of human infants and rats using novel paradigms, we plan to examine the precision, modality-independence, and ordinal nature of these representations. Asking questions such as: Do preverbal infants share with non-human animals this magnitude system for representations of time, number, and size? Are these magnitudes stimulus-dependent (and thus perceptually-bound)? Are quantity discriminations in these nonverbal populations based upon inherent knowledge that one value is greater than the other? In addressing such issues, I hope to provide a greater understanding of these nonverbal quantity representations, thus leading to the development of earlier clinical behavioral screens.